Various methods have been applied to remove uranium and other contaminants from aqueous solution. An established method involves inorganic or organic ion exchange resins. Ion exchange processes are generally most effective at high concentrations of uranium in solution, but less effective at relatively low concentrations of uranium, in the 0-20 ppm range, due to their reversibility. Ion exchange processes thus do not have the capacity to effect final clean up of dilute uranium-contaminated bodies of water, bringing them within water quality standards adopted by the U.S. federal government (100 parts per billion), the Canadian federal government (40 parts per billion) and other jurisdictions that have stringent water quality rules.
Electrodialysis and reverse osmosis have also been employed for removal of uranium and other contaminants, but are considered very expensive because they generally require large quantities of electrical power.
Wetland remediation has also been used, in the sense that mosses and grasses in a wetland environment have been used to remove uranium from contaminated water introduced into the wetland. A problem with this method is that the uranium remains in the wetland after remediation is completed. In wetland remediation, the uranium is absorbed by plants and land in and around the wetland area, contaminating them. Also, there is some indication that, at night, when the temperature drops, the wetland releases the uranium back into the water. In other words, this process appears to be reversible.
Certain types of bacteria have been used to remove uranium and other contaminants from solution. Bacteria require a nutrient medium to grow and reproduce. Accordingly, they may require a sterile environment, because they may be prone to competition with other biological contaminants that consume the nutrient medium. Also, certain bacteria do not grow well in alkaline environments, and so would not work well in uranium-contaminated water having a high pH. Some bacteria may be regarded as unsafe for human operators. Further, to the extent the bacteria have been genetically modified, there is additional cost involved in development and production and regulation of the genetically modified bacteria.
Dead algal biomass has been used in a limited way to remove uranium from solution. In addition, it has been recognized that live photosynthetic algae remove uranium from solution. It is understood, however, that little effort has been made to adapt photosynthetic algae in a system and method for large scale removal of uranium, similar radioactive constituents, and other contaminants from water in field and industrial conditions.